1. Technical Field of the Invention
The present invention relates to sunscreen compositions comprising, formulated into a cosmetically acceptable carrier, at least one system for screening out UV radiation, and containing:                (a) at least one insoluble organic UV-screening agent,        (b) at least one specific hydroxyalkylurea compound.        
This invention also relates to the formulation of a hydroxyalkylurea compound of specific formula into a composition in the form of an emulsion, comprising at least one water-soluble UV-screening agent, for improving the comfort after application, in particular the softness to the touch.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation with wavelength of from 280 nm to 400 nm permits tanning of the human epidermis and that rays with wavelengths of from 280 to 320 nm, which are known as UV-B rays, cause skin burns and erythema that can harm the development of a natural tan; this UV-B radiation should therefore be screened out.
It is also known that UV-A rays, with wavelengths of from 320 to 400 nm, which cause tanning of the skin, are liable to induce an impairment in the skin, especially in the case of sensitive skin or skin that is continually exposed to solar radiation. UV-A rays in particular bring about a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging. They promote the triggering of the erythemal reaction or amplify this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. It is therefore desirable also to screen out UV-A radiation.
UV-A and UV-B rays should therefore be screened out, and cosmetic compositions for protecting the human epidermis containing UV-A- and UV-B-screening agents currently exist.
These anti-sun compositions are quite often in the form of an emulsion, of oil-in-water type (i.e., a cosmetically and/or dermatologically acceptable carrier consisting of a continuous aqueous dispersing phase and of a discontinuous fatty dispersed phase), or of water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contains, in varying concentrations, one or more conventional lipophilic organic screening agents and/or conventional hydrophilic organic screening agents capable of selectively absorbing the harmful UV radiation, these screening agents (and the amounts thereof) being selected as a function of the desired sun protection factor, the sun protection factor (SPF) being expressed mathematically as the ratio of the dose of UV radiation required to reach the erythema-forming threshold with the UV-screening agent to the dose of the UV radiation required to reach the erythema-forming threshold without the UV-screening agent. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
The UV-screening agents most commonly used are organic and soluble in oils or in aqueous media; they generally have, within their structure, a chromophore group linked to a solubilizing group, which is generally a fatty chain in the case of liposoluble UV-screening agents or else a carboxylic or sulfonic acid group in the case of water-soluble UV-screening agents.
The prior art describes micronized insoluble organic UV-screening agents with a mean particle size ranging from 10 nm to 2 μm, which have the advantage of being more effective than their soluble homologues comprising the same chromophore group to an equivalent degree. UV-screening agents of this type are in particular described in EP-746,305 and EP-8-405,395. However, certain anti-sun formulations containing this type of screening agent have a tendency, after application, to make the skin rough.
Another difficulty lies in the fact that anti-sun emulsions based on insoluble UV-screening agents, after application to the skin, produce an uneven, nonhomogeneous, or even coarse, distribution of the insoluble UV-screening agents on the skin, which may be harmful to the quality of the desired overall protective effect. This poor distribution that is observed at the surface of the skin is often linked to the fact that, in terms of the emulsion, there is a substantial lack of homogeneity after application.